使用 OpenCSV 将Java Bean 映射到 CSV

将Java Bean（对象）转换为 CSV 文件的需求非常普遍，有很多方法可以将 Bean 写入 CSV 文件，但将Java Bean 映射到 CSV 的最佳方法之一是使用 OpenCSV 库。在 OpenCSV 中有一个类名StatefulBeanToCsvBuilder ，它有助于将Java Bean 转换为 CSV。

1. 第一个任务是将 OpenCSV 库添加到 Project中。
   • 对于 maven 项目，在 pom.xml 文件中包含 OpenCSV maven 依赖项。

     
         com.opencsv
         opencsv
         4.1
     
     

   • 对于 Gradle 项目，包括 OpenCSV 依赖项。

     compile group: 'com.opencsv', name: 'opencsv', version: '4.1'

   • 您可以下载 OpenCSV Jar 并包含在您的项目类路径中。
2. 将 JavaBean 映射到 CSV
   以下是将Java Bean 映射到 CSV 的分步过程。
   1. 创建用于将数据写入 CSV 文件的 Writer 实例。

      Writer writer = Files.newBufferedWriter(Paths.get(file_location));

   2. 创建需要写入 CSV 文件的对象列表。
   3. 使用 ColumnPositionMappingStrategy 将 Created 对象的列映射到 csv 的列。
      这是一个可选步骤。如果不使用 ColumnPositionMappingStrategy，那么对象将被写入 csv，其列名与对象的属性名相同。

      ColumnPositionMappingStrategy mappingStrategy = new ColumnPositionMappingStrategy();
          mappingStrategy.setType(Employee.class);
      
      where Employee is the object to be mapped with CSV.
      

   4. 创建StatefulBeanToCsvBuilder后，调用StatefulBeanToCsvBuilder类的build方法创建StatefulBeanToCsv类的对象，以writer对象为参数。用户还可以根据需要提供：
      • ColumnPositionMappingStrategy借助 StatefulBeanToCsvBuilder 对象的withMappingStrategy函数。
      • 借助StatefulBeanToCsvBuilder对象的withSeparator函数生成的 csv 文件的分隔符。
      • 借助StatefulBeanToCsvBuilder对象的withQuotechar函数生成 csv 文件的withQuotechar 。

      StatefulBeanToCsv beanToCsv = new StatefulBeanToCsvBuilder(writer)
      .withMappingStrategy(mappingStrategy)
      . withSeparator('#')
                          .withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)
                          .build();
      

   5. 创建 StatefulBeanToCsv 类的对象后，您可以借助 StatefulBeanToCsv 对象的 write 方法将对象或对象列表添加到 csv 文件中。

      beanToCsv.write(Employeelist);
      

示例：在此示例中，我们将创建具有名称、年龄、公司、工资等属性的 Employee 对象列表。然后我们将生成一个包含 Employee 对象的 CSV 文件Employees.csv。
代码：

1. 员工。Java

   public class Employee {
     
       public String Name, Age, Company, Salary;
     
       public Employee(String name, String age, 
                   String company, String salary)
       {
           super();
           Name = name;
           Age = age;
           Company = company;
           Salary = salary;
       }
     
       @Override
       public String toString()
       {
          return "Employee [Name=" + Name + ", 
          Age=" + Age + ", Company=" + Company + ", 
          Salary=" + Salary + "]";
       }
   }
   

2. BeanToCSV。Java

   import java.io.FileWriter;
   import java.io.Writer;
   import java.nio.*;
   import java.nio.file.Files;
   import java.nio.file.Paths;
   import java.util.*;
   import com.opencsv.bean.ColumnPositionMappingStrategy;
   import com.opencsv.bean.StatefulBeanToCsv;
   import com.opencsv.bean.StatefulBeanToCsvBuilder;
     
   public class BeanToCSV {
       public static void main(String[] args)
       {
     
           // name of generated csv
           final String CSV_LOCATION = "Employees.csv ";
     
           try {
     
               // Creating writer class to generate
               // csv file
               FileWriter writer = new 
                          FileWriter(CSV_LOCATION);
     
               // create a list of employee
               List EmployeeList = new 
                                    ArrayList();
               Employee emp1 = new Employee
                        ("Mahafuj", "24", "HTc", "75000");
               Employee emp2 = new Employee
                     ("Aman", "24", "microsoft", "79000");
               Employee emp3 = new Employee
                       ("Suvradip", "26", "tcs", "39000");
               Employee emp4 = new Employee
                        ("Riya", "22", "NgGear", "15000");
               Employee emp5 = new Employee
                       ("Prakash", "29", "Sath", "51000");
               EmployeeList.add(emp1);
               EmployeeList.add(emp2);
               EmployeeList.add(emp3);
               EmployeeList.add(emp4);
               EmployeeList.add(emp5);
     
               // Create Mapping Strategy to arrange the 
               // column name in order
               ColumnPositionMappingStrategy mappingStrategy=
                           new ColumnPositionMappingStrategy();
               mappingStrategy.setType(Employee.class);
     
               // Arrange column name as provided in below array.
               String[] columns = new String[] 
                       { "Name", "Age", "Company", "Salary" };
               mappingStrategy.setColumnMapping(columns);
     
               // Creating StatefulBeanToCsv object
               StatefulBeanToCsvBuilder builder=
                           new StatefulBeanToCsvBuilder(writer);
               StatefulBeanToCsv beanWriter = 
             builder.withMappingStrategy(mappingStrategy).build();
     
               // Write list to StatefulBeanToCsv object
               beanWriter.write(EmployeeList);
     
               // closing the writer object
               writer.close();
           }
           catch (Exception e) {
               e.printStackTrace();
           }
       }
   }
   

输出：

EmployeeData.csv
CSV file contains:-----

"Mahafuj", "24", "HTc", "75000"
"Aman", "24", "microsoft", "79000"
"Suvradip", "26", "tcs", "39000"
"Riya", "22", "NgGear", "15000"
"Prakash", "29", "Sath", "51000"

参考： BeanToCsv 官方文档